Carbon black is generally used as a support of a fuel cell catalyst. However, when carbon black is used as a support, there occurs a problem with the durability due to the corrosion of carbon.
In order to alleviate the problem, studies on carbon nanotube (CNT), carbon nanofiber (CNF), carbon nanocage (CNC), and the like, which are crystalline carbon forms having a high corrosion resistance, have been actively conducted. However, these crystalline carbon forms have a problem in that these carbon forms are not dispersed well in a polar solvent due to the strong surface water repellency thereof. For this reason, there is a problem in that platinum is agglomerated without being uniformly dispersed in the process of loading platinum into a carbon support.
In order to solve the problem, an acid treatment method in which the surface of carbon is oxidized to attach a function group to the surface has been widely used (Chem. Eur. J., 8, 1151). In the acid treatment method, a strong acid such as nitric acid, sulfuric acid, or a mixed solution of nitric acid and sulfuric acid is used, and a functional group including oxygen such as a carboxyl group (—COOH), a hydroxyl group (—OH), and a carbonyl group (>C═O) is formed on the surface of carbon. Due to the functional group thus formed on the surface of carbon, the hydrophilicity is increased to provide a deadlock point of platinum ions and the solubility in a polar solvent is increased to enhance the dispersibility of platinum.
However, there is a problem in that the surface treatment of crystalline carbon using an acid treatment damages the surface of crystalline carbon, and thus reduces corrosion resistance of crystalline carbon, and the durability deteriorates. Therefore, an acid treatment method using a strong acid is advantageous in supporting a catalyst, but has a limitation of reducing the durability of a catalyst of a fuel cell by increasing the corrosion of carbon.